1. Field of the Invention
The present invention relates to an image recording apparatus such as a laser printer, and particularly to an improved apparatus for detecting a start of scan (SOS) signal to true up starting positions of respective line images.
2. Description of the Related Art
In a conventional laser printer, a laser beam outputted from a semiconductor laser which is driven according to image data is deflected by a deflecting surface of a polygon mirror rotated by a motor and the deflected laser beam is projected on a photoconductor drum so that the image data is recorded on the photoconductor drum in the unit of one scan line.
In a conventional laser printer, a photodiode for detecting the SOS signal is arranged at a predetermined position which is chosen so as not to interface with the laser beam during each scan for writing the line data on a photoconductor means such as a photoconductor drum. When the laser beam deflected by the deflection means passes the photodiode, an SOS signal is outputted to start the writing of each data.
In another conventional laser printer, there is provided an optical fiber, one end of which is positioned at the predetermined position for the photodiode in the above mentioned laser printer, and a photodiode which is connected to the other end of the optical fiber in order to detect the laser beam therethrough. On the other hand, one more photodiode is provided for monitoring the light amount of the laser beam emitted from the semiconductor laser which varies according to the temperature thereof.
Accordingly, in the conventional laser printer, there is generally provided at least two photodiodes, one for detecting the SOS signal and the other for monitoring the light amount of the laser beam.